As is well known to those skilled in the art, middle distillate fuels such as aviation jet fuels form gums and deposits on storage, particularly when storage is at elevated temperature. These gums and deposits are undesirable in that they may interfere with operation by partially or wholly clogging narrow passageways through which the fuel is to pass. The standard test method for determining the amount of thermal degradation products of middle distillate hydrocarbon fuels such as Jet Fuels is ASTM, Jet Fuel Thermal Oxidation Test D-3241. In this JFTOT test, a fuel is maintained at elevated temperature; and the amount of gum and deposit is determined. The results are measured in terms of the amount of deposit on an aluminum heater tube and the rate of plugging of a 17 .mu.m nominal porosity precision filter; and a visual rating of 0-2 is good and 3-4 is unsatisfactory by comparison with a standard. Preliminary screening testing may be carried out using a test temperature of 400.degree. F. (in a Modified JFTOT Test) rather than the standard temperature of 500.degree. F.
It is an object of this invention to improve the thermal stability of a middle distillate. Other objects will be apparent to those skilled in the art.